The present invention relates to a power generation system of a fuel cell including a temperature control device for a hydrogen supply unit therein. In this system, the fuel cell receives hydrogen from the hydrogen supply unit and oxygen from an oxygen supply unit, for power generation. Then, unconverted gas discharged from the fuel cell is employed as a heat source for the hydrogen supply unit.
In recent years, due to improvement in electrochemical characteristics of a solid polymer membrane, implementation of a household polymer membrane fuel cell system as an on-site type distributed power source has been expected. When this household fuel cell system is commercialized, a higher efficiency than that of a conventional power generation system is expected. Thus, various proposals have been made to achieve the higher efficiency.
As an example of the polymer membrane fuel cell power generation system, there is well known the system in which hydrocarbon fuel is reformed to produce hydrogen and carbon monoxide is removed from the reformed gas in a reformer, and the resulting gas is then supplied to the fuel cell. Then, the fuel cell consumes hydrogen in the reformed gas and oxygen in air, thereby performing power generation. Unconverted gas discharged from the fuel cell is used as the heat source for reforming the hydrocarbon fuel by the reformer.
In this power generation system, a reformed-gas system of the power generation system is configured to include the reformer, the fuel cell, a heat exchanger and the like. In order to operate the system with the higher efficiency, the reformed gas is delivered from the reformer and circulates through the fuel cell, the heat exchanger and the like, and the combustion unit of the reformer again. In this configuration, the reformed-gas system becomes a closed system. Accordingly, when some disturbance is caused, the amount of heat to be supplied to the combustion unit of the reformer will be changed. As such disturbance, a fluctuation in the amount of the gas supplied, changes in the amount of hydrogen produced and the chemical composition of the reformed gas due to degradation of a catalyst in the reformer, a change in an outside air temperature, and the like can be pointed out. This system, however, has no buffering mechanism for stabilizing the power generation system. Thus, when the some disturbance is given, it becomes considerably difficult to operate the power operation system with stability.
Then, in order to address the problem described above, JP-A-8-255621 discloses a technique for controlling the temperature of the reaction unit of a reformer. In this technique, a fuel cell main body is divided into a plurality of portions, and the divided fuel cell portions are arranged in series. Fuel off-gas from a divided fuel cell portion in the last stage is supplied to the burner of the reformer. Thus, by controlling the generated power of the divided fuel cell portion in this last stage, the temperature of the reaction unit of the reformer is controlled.
In the technique disclosed in JP-A-8-255621, however, the fuel cell main body must be divided into the plurality of the portions. Accordingly, the configuration of the system becomes complicated.